A. Field of the Invention
This invention relates to a method and apparatus for restoring and/or maintaining an underground aquifer water supply system wherein the output flow has fallen significantly below optimum levels because of plugging of the aquifer with flow impeding deposits which have accumulated in the porous substrate of the waterbed.
It especially relates to a process and system which minimizes or entirely eliminates the need for well downtime during treatment and allows design of a restoration or maintenance procedure which is specific for each problem well encountered depending on the nature of the flow impeding materials which have accumulated in the aquifer.
B. Description of the Prior Art
It is known that ground water in some locales has an excessive content of iron and manganese. The quality of the water can vary greatly over small distances. In those cases where the iron and manganese content of the ground water are so high to preclude effective usage thereof, it is necessary that these metals be removed before the water can be employed for drinking or industrial purposes.
It is further known that iron occurs in two states of oxidation in an aquifer--the divalent (ferrous) and trivalent (ferric) forms. U.S. Pat. No. 3,649,533 discloses a process for increasing the amount of oxygen available in the strata around a producing well whereby iron and manganese oxidixing bacteria assist in oxidation of the ferrous iron and also enhance oxidation of the manganese. In accordance with the process of the patent, a number of aeration wells are placed in a ring around the supply well. Water which has been enriched with oxygen or an oxygen supplying agent is forced down the aeration wells as a slug of water which then disperses into the aquifer surrounding the production well casing. The oxygen-rich water provides a suitable habitat for the iron and manganese oxidizing process. It is taught that the water slug treatment should be carried out at infrequent, extended intervals depending upon the amount of undesirable iron and manganese compounds in the water to maintain a certain maximum level of such constituents in the water. It is indicated that the precipitation of iron in the aquifer has only a slight effect on strata permeability. Cloggage of the aquifer surrounding the well is not thought to occur for a period of time much longer than the life span of a typical well.
It has also been proposed in the past to remove a quantity of water from the producing well, collect the same in a treatment vessel, add a chemical agent thereto, and then pump such treated water as a slug back down into the well through the well casing so that the treatment composition may then slowly spread out into the aquifer for a predetermined distance from the casing intake. Generally, the water is finally pumped out of the aquifer and the level of treatment agent therein monitored until it has fallen to an acceptable level. Until this low level concentration is reached though, the water must be directed to effluent.
General fundamentals of water well operation and maintenance are described in an article by E. W. Bennison, March 1953 publication of the Journal of A.W.W.A. commencing at page 252. In that article, the author describes the three most common causes for well failure. Two of the problems are primarily mechanical in nature in connection with the well equipment and its operation, while the third involves deterioration of the well during its life due in part to accumulation of flow impeding agents in the aquifer surrounding the production casing.